1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus, such as a copying apparatus, a laser beam printer or a facsimile apparatus and, in particular, to a cleaning means to be used in such an image forming apparatus.
2. Description of the Related Art
Conventionally, there have been proposed various image forming apparatuses which are equipped with a plurality of image forming sections and in which toner images of different colors are formed in the image forming sections, the toner images being sequentially superimposed one upon the other on the same recording material to thereby provide a color image.
In such a color image forming apparatus, foreign matter such as toner, lubricant oil or dust is usually allowed to adhere to the image carrier for carrying toner images formed thereon, the recording material carrying member for carrying the recording material and guiding it to the transfer section where image transfer from the image carrier is effected, etc. Such foreign matter, which may contaminate the recording material, must be removed by cleaning.
When the image forming speed of the image forming apparatus is relatively high, or when the amount of lubricant oil is increased as a result, for example, of using a sharp melt type toner, which is described below, a higher level of cleaning performance is required.
An electrophotographic multi-color copying machine of the type which uses an endless recording material carrying member is in use for high-speed recording.
In such an image forming apparatus, the recording material, which is carried by a feeding belt constituting the recording material carrying member, is conveyed to the transfer position of each of a plurality of image carriers (photosensitive drums). Then, cyan, magenta, yellow and black toner images are transferred one by one from the respective image carriers to the recording material carried by the feeding belt. After the image transfer has been completed, the recording material is conveyed to a fuser, where the toners of these colors are melted and mixed with each other, whereby a full-color toner image is fixed to the recording material. The fuser is equipped with a fixing roller which is held in contact with the unfixed toner image on the recording material, and a pressurizing roller which is in contact with the other side of the recording material. A lubricant such as silicone oil is applied to the fixing roller in order to prevent toner from adhering thereto.
After the completion of image transfer, the portion of toner remaining on the feeding belt and any foreign matter thereon are removed by cleaning by using a cleaning member which is brought into contact with the surface of the feeding belt.
However, the above construction has a problem in that the portion of the feeding belt where there is no recording material is subject to contamination with toner during the image transfer process. For example, some of the toner on the photosensitive drum may be scattered on this portion due to pretransfer discharge, which occurs immediately before the transfer position, or some of the unfixed toner transferred to the recording material may be scattered on this portion of the belt at the time of separation from the photosensitive drum. Further, fog toner on the photosensitive drum may be transferred to the belt, or toner may be allowed to drop directly onto it from the developing device or the cleaner for the photosensitive drum.
A cleaning member for removing toner adhering to the conveying belt, for example, a cleaning web (made of a nonwoven fabric) is attached to the surface of the conveying belt. As compared with the case in which copying is performed on a single sheet, the case in which copying is successively performed on a plurality of sheets has a problem in that a large amount of toner is allowed to remain on the belt in a short time. The amount of toner remaining on the belt depends upon the number of sheets on which copying is performed. Thus, in the latter case, an improvement in cleaning performance is required.
Further, in high-speed apparatuses, full-color apparatuses or the like, when the high voltage for image transfer is applied to the transfer charger even during inter-sheets periods (time intervals between sheets in the case of successive copying) in order to simplify the control sequence, the fog toner on the photosensitive drum is easily allowed to be transferred.
Further, to maintain satisfactory fixing conditions, when the thickness of the recording material is large, the fixing speed is decreased as compared to the usual case and, at the same time, the intervals between sheets in successive copying is enlarged. Further, due to the difference in size of the recording material, for example, the difference in size between an A4 size paper and a post card, a difference is generated in terms of the toner contamination of the feeding belt (as a result of scattering of unfixed toner images on the recording material) in the thrust direction thereof (the direction which is perpendicular to the direction in which the belt runs).
Further, in a both-side type machine which is capable of forming images on both sides of a recording material, the oil adhering to the recording material during the fixing on the first surface of the recording material is allowed to be transferred to the feeding belt during the image transfer on the second surface of the recording material. Since the oil easily comes into close contact with the remaining toner on the feeding belt, it is difficult to remove the oil and toner by cleaning. According to a measure for preventing this oil from being transferred to the photosensitive drum, the photosensitive drum is constantly coated with toner, which toner functions as a spacer between the photosensitive drum and the feeding belt. However, this results in the amount of toner transferred to the feeding belt being increased accordingly.
When the next recording material is attracted to the feeding belt without having clearing away such residual toner contamination on the feeding belt, the residual toner is transferred to the back side of the recording material and fixed thereto. Accordingly, a backside of the copy image whose back side becomes contaminated. This problem has not been solved yet. In an apparatus having a both-side copying function, image formation is also performed on the back side of the recording material, which is contaminated with the residual toner, with the result that the images formed on the first and second sides are both defective images contaminated with residual toner.